(1) Balamurali Ambati was a very smart child. (2) He studied twice as fast as other kids his age. (3) When he was 11 years old, he finished high school. (4) Then, he went to college. (5) He earned a four-year degree in only two years. (6) At age 17, he became the world's youngest doctor. Which sentence is the topic sentence of the paragraph? A. sentence 5 B. sentence 1 C. sentence 6 D. sentence 2